An evaporated gas treatment system of a vehicle enables the evaporated gas volatilized in a fuel tank to temporarily adsorb on a canister, and introduces the gas into the engine for recombustion using the engine negative pressure, thereby preventing the discharge of the gas to the outside. In recent years, the reduction of the engine operation frequency due to the trend of vehicles toward HEVs (Hybrid Electric Vehicles) or the like causes the reduction of the treatment capability of the evaporated gas treatment system using the engine negative pressure. In order to increase the flow rate of the evaporated gas to be supplied to the engine upon occurrence of the negative pressure corresponding to the reduction of the engine operation frequency, there has been a demand for a higher flow rate of the electromagnetic valve to be disposed at the path establishing a communication between the canister and the engine.
However, the higher flow rate of the electromagnetic valve causes a variety of detriments such as the scale-up of the base, and the degradation of the low-flow-rate precision (flow rate resolution). Therefore, in the past, a parallel arrangement of electromagnetic valves with a low flow rate enables a high-flow-rate control (for example, see Patent Documents 1 and 2). The use of a plurality of electromagnetic valves enables the improvement of the controllability owing to the enhancement of the flow rate resolution as compared with the case where a higher flow rate is controlled by a single electromagnetic valve. Particularly, in Patent Document 1, a positive suction type electromagnetic valve and a reverse suction type electromagnetic valve are arranged in parallel; in a lower flow rate region in which there may occur a phenomenon referred to as jumping such that the flow rate rapidly increases or decreases upon valve opening, only the reverse suction type is driven, and also in a higher flow rate region than the lower flow rate region in which no jumping substantially occurs, both of the positive suction type and the reverse suction type are driven to suppress the jumping; thus, it is contemplated that the lower flow rate precision is improved.
The higher flow capacity of the electromagnetic valve also raises pulsating sounds caused by a flow of air. For this reason, as a countermeasure against the pulsating sound upon the higher flow rate, in the past, a large capacity chamber is inserted between the ports of the electromagnetic valves; however, layout property thereof is deteriorated. Therefore, in Patent Document 1, two electromagnetic valves are inserted in the chamber to be included therein, and when operation timings thereof are changed, it is contemplated to synthesize and cancel the pressure fluctuations caused by the opening/closing operations of the electromagnetic valves.